Heretofore, electronic parts such as diodes, transistors and integrated circuits are sealed mainly with epoxy resin compositions. The epoxy resin compositions contain fire retardants containing a halogen and an antimony compound to provide the composition with the flame retarding property. The flame retarding property of the composition is exhibited by generation of a gas of a halogen or an antimony halide at high temperatures.
However, in accordance with the above method for exhibiting the flame retarding property, a gas of a halogen or an antimony halide is generated when an electronic part is exposed to a high temperature and this causes a big problem in that corrosion of aluminum circuits and fracture of connecting portions between aluminum pads and gold wires in chips take place. Moreover, it is required for protection of the environment and the health that an epoxy resin composition which does not use any fire retardants containing a halogen or an antimony compound and exhibits an excellent flame retarding property be developed.
To overcome the above problems, a resin composition having a glass transition temperature higher than the temperature of the environment which is obtained by a combination of an epoxy resin and a phenol resin curing agent is used to decrease diffusion of a gas of a halogen or an antimony halide during storage at high temperatures and high temperatures storage life can be improved. Alternatively, an ion scavenger may be added to scavenge gases of a halogen or an antimony halide generated during storage at high temperatures. A combination of these methods may also be used.
On the other hand, recently, electronic parts are often disposed at the surface of substrates of circuits. The size of electronic parts are becoming smaller and thinner. Therefore, improvement in crack resistance is required in soldering for attachment of electronic parts to substrates of circuits. Thus, an epoxy resin composition exhibiting both of excellent crack resistance in soldering and excellent high temperatures storage life has been desired. However, even when an epoxy resin composition which contains a fire retardant of a halogen compound or a combination of a halogen compound and an antimony compound and exhibits excellent crack resistance in soldering is used, addition of an ion scavenger cannot provide sufficient high temperatures storage life when the epoxy resin composition has a low glass transition temperature. On the other hand, an epoxy resin composition shows insufficient crack resistance in soldering when the epoxy composition has a high glass transition temperature. No epoxy resin compositions which have a low glass transition temperature and exhibit excellent high temperatures storage life have been provided.
Various fire retardants other than fire retardants containing a halogen and antimony compounds have been studied. For example, metal hydroxides such as aluminum hydroxide and magnesium hydroxide and boron compounds have been studied. However, these compounds do not effectively exhibit the flame retarding property unless they are used in a large amount. Moreover, these compounds contain large amounts of impurities and reliability in a humid condition is not satisfactory. Therefore, these compounds are not practically used. Fire retardants containing red phosphorus are effective even when these fire retardants are used in small amounts and are useful for fire retardation of epoxy resin compositions. However, red phosphorus has a problem in reliability in a humid condition because red phosphorus reacts with a minute amount of water to form phosphines and corrosive phosphoric acid. An epoxy resin composition which exhibits both of the flame retarding property and the reliability in a humid condition without using a fire retardant containing a halogen or an antimony compound has been desired.
The present invention has an object to provide an epoxy resin composition for sealing semiconductors which does not contain any halogen compounds or antimony compounds, has an excellent flame retarding property and exhibits excellent high temperatures storage life and reliability in a humid condition, and to provide a semiconductor device using this epoxy resin composition.